Papers by Author: Hiroaki Mori

Abstract: Recently, stress corrosion cracking (SCC) of primary piping of stainless steel has been observed. SCC is considered to initiate and progress at near the welding zone in butt-welded pipes, because of the tensile residual stress introduced by welding. In present work, three-dimensional and axisymmetric thermo-elastic-plastic finite element analyses have been carried out, in order to clarify the effect of geometrical and welding conditions on through-thickness residual stress. In particular, butt-welding joints of SUS316L pipes have been examined. The residual stress was simulated by three-dimensional and axisymmetric models and the results were compared and discussed in detail.

Abstract: In order to extend the life of petroleum pressure vessels operated in long term, it is demanded to establish the repair welding technique. To make clear the effect of weld thermal cycles during repair welding on the hydrogen content and weld cold cracking at the base metal of 2.25Cr- 1Mo steel / overlaying metal of austenitic stainless steels interface in the structural material of petroleum pressure vessels, the crack susceptibility was estimated by y-groove weld cracking test and repair welding test with varying overlay thickness and hydrogen exposure conditions. In addition, the hydrogen distribution in the material was calculated by the theoretical analysis using the diffusion equation based on activity. The crack susceptibility was raised with increase in the hydrogen content at the interface. It was concluded that the cracking could be prevented by controlling the repair welding process to reduce the hydrogen content at the interface.

Abstract: Quenching of the nanocrystalline high-pressure e phase of iron, which has not been observed under a conventional shock compression, was attained using a femtosecond laser. A small quantity of the g phase of iron also existed. We found that the e phase was induced by the shock itself but not the g phase. The g phase was suggested to be induced as an intermediate structure between the a-e transition. The femtosecond laser driven shock may have the potential to quench high-pressure phases which has not been attained using conventional methods.